1. Field of the Invention
The present invention generally relates to a technique for positioning an optical system element. In particular, the present invention relates to a technique for positioning of a projection optical system element (lens, mirror, or the like) of an exposure apparatus used in a process for fabricating various devices including a semiconductor chip such as an IC or an LSI, a display device such as a liquid crystal panel, a detection device such as a magnetic head, and an image pickup device such as a CCD, and an exposure apparatus using the projection optical system. The present invention is suitable for, for example, positioning an optical system element in an exposure apparatus using extreme ultraviolet (EUV) light as exposure light (hereinafter referred to as “an EUV exposure apparatus”).
2. Related Background Art
A semiconductor exposure apparatus is an apparatus for transferring a large number of original plates (reticles) having different kinds of patterns onto a silicon wafer (substrate). When a high integration circuit is produced, it is essential to improve not only a resolution performance but also overlay precision.
Overlay errors in the semiconductor exposure apparatus are classified into an alignment error, an image distortion, and a magnification error. The alignment error can be reduced by adjusting a relative displacement between the original plate (reticle) and the substrate (wafer). On the other hand, the image distortion and the magnification error can be adjusted by moving at least one optical element which is a part of an optical system. When the optical element is moved, it is necessary to prevent a parallel decentration amount and a tilt decentration amount from increasing.
Up to now, there has been proposed an exposure apparatus in which a sensor for continuously detecting a distance from a fixed portion to an optical element is provided to control the posture of the optical element in real time (for example, see Japanese Patent Application Laid-Open Nos. 2000-357651 and 2002-131605). There has been also known a positioning control mechanism for controlling the six axes of an optical element (for example, see Japanese Patent Application Laid-Open No. 2001-231077).
In recent years, in order to obtain a necessary imaging relationship while a resolution of a semiconductor device pattern, higher drive positioning precision for correcting a position, posture precision, aberration, and the like is being required for the optical element as compared with a conventional case. As a factor deteriorating such positioning precision, there is a disturbance. In conventional positioning control, an influence of the disturbance can be ignored. However, with higher positioning precision being demanded, the influence of the disturbance cannot be ignored. According to, for example, Japanese Patent Application Laid-Open Nos. 2000-357651 and 2002-131605, when a disturbance is transmitted from a floor or the like to a lens barrel in the device for controlling the positioning of the optical elements to only the fixed portion or the lens barrel, the respective optical elements randomly vibrate to cause a synchronization error. Therefore, a problem occurs in that the required imaging performance cannot be obtained.